The present invention relates to an apparatus and method for identifying tires and to an apparatus and method for evaluating road surface conditions. More particularly, it relates to an apparatus and method for identifying tires for identifying a driving stiffness level of tires which is applicable for controlling a vehicle or for improving safety of the vehicle, as well as to an apparatus and method for evaluating road surface conditions for identifying presently mounted tires in case the tires have been exchanged and for suitably setting a threshold for determining a tendency of slip.
Tires are engraved with longitudinal grooves as well as lateral grooves in view of water drainage such that rubber blocks surrounded by these grooves are formed. In case these rubber blocks are large, shear deformation in front and rear, and right and left directions hardly occurs and further exhibits a large rigidity, and tires having tread patterns composed of large blocks are generally referred to as tires of a large pattern rigidity.
Since the degree of pattern rigidity largely affects slip rates in addition to cornering power and cornering force, it is important to know the pattern rigidity of tires for estimating behaviors of a vehicle on the basis of rotational information of the tires in devices aimed to improve performance and safety of the vehicle on the basis of rotational information of the tires such as an ABS (anti-lock braking system), a TCS (traction control system) or an apparatus for alarming decrease in tire air-pressure. It is generally the case that summer tires are of large pattern rigidity while winter tires are of small pattern rigidity.
A conventional apparatus for alarming decrease in air pressure for detecting a decrease in internal pressure of tires on the basis of changes in rotational speeds of tires is so arranged that it applies the fact that a decrease in air pressure of a tire causes a decrease in dynamic load radius of the tire such that its rotational speed is increased when compared to tires of normal air pressure. Japanese Unexamined Patent Publication No. 149119/1995 is one exemplary publication which suggests a method for detecting a decrease in internal pressure based on a relative difference between rotational speeds of tires. Since the rotational speed of tires is affected through factors such as turning movements, acceleration/deceleration, load or speed of the vehicle, various measures are being taken for eliminating influences thereof. It is further the case with such apparatuses for alarming decrease in tire air-pressure that tuning of vehicle factors such as correction coefficients at the time of turning movements is performed to suit tires which are mounted to a new vehicle. However, in case tires have been exchanged from summer tires to winter tires or from winter tires to summer tires, which specifications largely differ from each other, estimations of behaviors of the vehicle will be largely shifted from those as set through the initial tuning and it might happen that no accurate information to be provided to the driver can be secured. Although it is known for a method in which initial tuning is performed by using summer tires and winter tires for setting average values thereof as vehicle factors, accuracy of detection of internal pressure will still be degraded.
It is thus deemed that a most suitable method is one which identifies whether the presently mounted tires are summer tires or winter tires, that is, which identifies degrees of pattern rigidities to automatically rewrite vehicle factors accordingly.
One example of a method for identifying differences in summer tires and winter tires is a method for measuring a rising gradient (driving stiffness) of a xcexc-s curvature of tires.
If it were possible to automatically identify whether the mounted tires are summer tires or winter tires in an apparatus for alarming decrease in internal pressure of tires, it would be possible to remarkably improve its detection accuracy. However, in case tires are to be identified on the basis of rising gradients of xcexc-s curvatures of tires, since such rising gradients will be varied not only through pattern rigidities of treads but also through friction coefficients of road surfaces, it is quite difficult to apply the same for identifying tires unless measures are taken such as restricting road surfaces for performing measurement.
On the other hand, there is another method for estimating tendency of slip (friction coefficient) between tires and road surfaces on the basis of rotational speed information of tires during running.
Such a method utilizes the fact that rising gradients of xcexc-s curvatures of tires and road surfaces differ depending on road surface friction efficiencies xcexc, wherein rotational speeds of wheels are periodically detected through, for instance, an ABS sensor for calculating slip ratios of front and rear wheels and acceleration of following wheels so as to obtain a gradient as a judged value. The obtained judged value is compared with a preliminarily set threshold for estimating a tendency of slip (road surface) xcexc. However, this threshold needs to be varied depending on stiffness of the tires or load applied onto the tires.
In order to cope with this problem, it would be possible to provide the vehicle with a switch for switching between summer tire mode and winter tire mode and to preliminarily set different thresholds for the summer tires and the winter tires which largely differ in stiffness from each other.
However, such switching between two types of modes might lead to a drawback that the accuracy of determining road surface conditions is degraded owing to the fact that differences in rising gradients exist also among summer tires (winter tires) depending on manufacturers or patterns, and that differences in rising gradients are also caused through wear conditions of tires.
The present invention has been made in view of the above-mentioned facts, and it is a first object thereof to provide an apparatus and method for identifying tires for identifying whether the presently mounted tires are summer tires or winter tires.
It is a second object thereof to provide an apparatus and method for evaluating road surface conditions for setting a threshold upon identifying presently mounted tires and accurately determining a tendency of slip.
In accordance with a first aspect of the present invention, there is provided an apparatus for identifying tires comprising: a rotational speed detecting means for periodically detecting rotational speeds of tires of four wheels of a vehicle; a first calculating means for calculating a vehicle speed based on a measured value obtained by the rotational speed detecting means; a second calculating means for calculating acceleration/deceleration of the vehicle; a third calculating means for calculating a slip ratio from the rotational speeds of the four wheels; a fourth calculating means for respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle; a fifth calculating means for obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratio; a sixth calculating means for calculating a tire identifying coefficient based on the linear regression coefficients of which correlation coefficients of are not less than a specified value; and a tire identifying means for identifying tires which is presently mounted based on the tire identifying coefficient.
In accordance with a second aspect of the present invention, there is provided a method for identifying tires comprising the steps of: periodically detecting rotational speeds of tires of four wheels of a vehicle; calculating a vehicle speed based on the measured rotational speed; calculating acceleration/deceleration of the vehicle; calculating a slip ratio from the rotational speeds of the four wheels; respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle; obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratio; calculating a tire identifying coefficient based on the linear regression coefficients of which correlation coefficients are not less than a specified value; and identifying tires which is presently mounted based on the tire identifying coefficient.
In accordance with a third aspect of the present invention, there is provided an apparatus for evaluating road surface conditions comprising: a rotational speed detecting means for periodically detecting rotational speeds of tires of four wheels of a vehicle; a first calculating means for calculating a vehicle speed based on a measured value obtained by the rotational speed detecting means; a second calculating means for calculating acceleration/deceleration of the vehicle; a third calculating means for calculating a slip ratio from the rotational speeds of the four wheels; a fourth calculating means for respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle; a fifth calculating means for obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratios; and a threshold setting means for setting a threshold for evaluating road surface conditions based on the linear regression coefficients of which correlation coefficients are not less than a specified value.
In accordance with a fourth aspect of the present invention, there is provided a method for evaluating road surface conditions comprising the steps of: periodically detecting rotational speeds of tires of four wheels of a vehicle; calculating a vehicle speed based on a measured value obtained by the rotational speed detecting means; calculating acceleration/deceleration of the vehicle; calculating a slip ratio from the rotational speeds of the four wheels; respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle; obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratios; and setting a threshold for evaluating road surface conditions based on the linear regression coefficients of which correlation coefficients are not less than a specified value.
In accordance with a fifth aspect of the present invention, there is provided a program for evaluating road surface conditions which makes a computer for evaluating road surface conditions function as a first calculating means for calculating a vehicle speed based on a measured value obtained by a rotational speed detecting means, a second calculating means for calculating acceleration/deceleration of the vehicle, a third calculating means for calculating a slip ratio from the rotational speeds of the four wheels, a fourth calculating means for respectively obtaining moving averages of the acceleration/deceleration and the slip ratios of the vehicle, a fifth calculating means for obtaining linear regression coefficients and correlation coefficients of the moving-averaged acceleration/deceleration of the vehicle and the slip ratios, and a threshold setting means for setting a threshold for evaluating road surface conditions based on the linear regression coefficients of which correlation coefficients are not less than a specified value.